However, new guidelines from a leading physicians' group suggest the
class you sit in on a plane may not raise your DVT risk, but your
proximity to the aisle might.

Sitting in a window seat is a risk factor for DVT, the
American College of Chest Physicians (ACCP) warn in their new advisory,
regardless of whether it's in economy or first class.

"DVT risk has nothing to do with economy class," said Dr. Gordon H.
Guyatt, chair of the ACCP panel that drafted the new guidelines.
"Really, the evidence is that actually where you sit isn't really an
issue. It's how much you move around. And if you're in a window seat
you are probably more willing to sit for long periods of time being
uncomfortable because you are reluctant to make anybody else move to
let you out."

The new recommendations are published in the February issue of CHEST.

DVTs are blood clots that typically occur in the legs. They can
become especially dangerous if they travel through the bloodstream to
the lungs, where they can form potentially lethal pulmonary embolisms.
The current guidelines, which are endorsed by a wide range of
American medical associations, are the ninth in a series of ACCP
updates on the issue. They were drafted after the panel extensively
reviewed findings from relevant studies published since the last update
in 2008.

Long-haul immobility does boost DVT risk, the experts noted. But as
the ACCP panel sifted through the evidence, they found no basis for the
notion of "economy class syndrome." Rather, folks in a window seat
might be more hesitant to get up and move around -- and that might
raise their odds for a DVT.

Still, "the first thing to say is that if you are a healthy person
you should not really worry about DVT because your risk -- even on a
long-term flight -- is considerably less than one in a thousand," said
Guyatt, who is also professor in the department of clinical
epidemiology and biostatistics at McMaster University in Hamilton,
Ontario, Canada. "So these guidelines are for those who have more than
a normal risk. For those who have had a clot before, or an abnormality
of their coagulation system, or disability that affects mobility. Or if
you are obese or have active cancer."

In addition to those risk factors, the ACCP says that air passengers
who are elderly, pregnant, take supplementary estrogen (including oral
contraceptives) or recently underwent surgery and/or trauma also face a
higher-than-normal risk for DVT.

Apart from seating considerations, the guidelines also suggest that
people on flights lasting six or more hours move about frequently and
stretch their calf muscles.

Higher-risk individuals should also wear graduated compression
stockings that stretch below the knee. Guyatt said it "would be crazy"
for passengers at normal risk to wear such stockings, and the ACCP
guidelines specifically argue against their use by healthy passengers.

The guidelines also generally discourage the taking of aspirin
and/or anticoagulant medications for the specific intent of lowering
DVT risk. That said, those at very high risk are encouraged to consult
their doctors in order to weigh the pros and cons of such drugs.

For his part, Dr. Christopher Cannon, a cardiologist at Brigham and
Women's Hospital in Boston, said the new DVT guidelines "make obvious
good sense."

"Getting up once every hour or two during a long flight and walking
up and down the aisle is what you want to do," he noted. "It's not
about class and the slight extra room you'll get in business. It's
about sitting by the window and looking over at the guy sleeping next
to you and thinking you'll wait rather than get up. That's the issue."

"I would also add that all of this would also apply to people taking
long car trips," Cannon said. "I've had tons of people driving home on
long car rides who have had problems with DVT. Hence the emphasis on
mobility. It's all about making sure you get up or get out and move."